I recently came across the photo below: part of a shipment of 366 Douglas motor cycles for Williams Bros in Sydney in April 1924. That's a lot of Douglases! Presumably most of the bikes were 2 3/4 side valves, but by this date Williams had already landed the first of the RA/RW/TW series of "Speed Model" OHV machines with the gearbox over the back cylinder. Not sure when the first OBs landed.
Leon
